Biochar has been widely studied to reduce multiple contaminant sources in one matrix (e.g., several heavy metals in soils), yet less attention has been paid to accelerating pesticide degradation while in the presence of any heavy metals, such as when kasugamycin (KSM) and cadmium (Cd) are both present in soil. While KSM has low toxicity compared to other pesticides, it can be a potential health risk when applied to vegetable crops, especially when KSM is used or overapplied to achieve rapid reductions in insect and disease pressure. The degradation behavior of KSM (2 kg ha−1) in the presence of Cd (20 mg kg−1) and biochar (5% by wt.) when growing spinach (Spinacia oleracea) was studied. The biochar increased spinach shoot and root biomass by 51.0–54.8% and 24.4–39.0%, respectively, compared to the KSM treatment only. Compared to the treatments that did not receive biochar, the biochar application increased the KSM degradation in the soil by 8.4–68.4% and, subsequently, less KSM was absorbed by the spinach roots (18.0–48.4%) and shoots (33.0–33.2%). The KSM degradation rate, as a function of soil depth, was enhanced in the presence of Cd. The biochar also effectively decreased the KSM concentration with soil depth, reducing downward KSM migration. The KSM degradation, increased by the biochar, led to smaller organic moieties and some macromolecular organic phases. In soils that are contaminated with Cd and where vegetables are raised, biochar may be used as an environmentally friendly proponent for increasing KSM degradation, reducing KSM downward transport and, thus, protecting environmental and human health.